A proposal is made to continue the investigations begun on the plasminogen activator content of human tumors and normal tissues obtained from surgery. The investigation was prompted by the results obtained by others that cells in culture, upon malignant transformation induced by oncogenic viruses or by chemical carcinogens, release large amounts of plasminogen activators into the culture medium. It was deemed essential to find out whether this phenomenon is also observable in human tumors growing in the host. In order to evaluate the significance of activator production, we are extracting plasminogen activators from malignant tumors, obtained freshly from surgery, and compare the amounts with those found in normal portions of the same tissue, removed at the same time. We are currently analyzing tumors from lung and from prostate. The lung tumors show significantly elevated activator levels, with very high values obtained from anaplastic carcinomas. The prostate study will have to await evaluation until a larger number of tumors are analyzed. In addition, we are also purifying activator from human lung (tumor and normal) and heart tissues in order to compare the activator with known activators, such as urokinase and kallikrein.